The present invention relates to a bending and tempering station for glass sheets, comprising a roll conveyor in which the relative vertical position of rolls is adjustable for arching the conveyor to a curvature corresponding to a desired degree of bending about a bending axis extending transversely to the glass sheet advancing direction i.e. parallel to the rolls, lower tempering boxes having top surfaces provided with tempering orifices, and upper tempering boxes having bottom surfaces provided with tempering orifices, said tempering boxes being movable for bringing said top and bottom surfaces in conformity to the arching of the conveyor. This type of apparatus is prior known from the U.S. Pat. Nos. 4,881,962 and No. 5,057,137. This apparatus has proved extremely useful in the production of bent and tempered construction glass.
In this prior known apparatus, the bending of a glass sheet is based on gravitational bending in a bending and tempering station located outside a heating furnace. Therefore, it is sometimes necessary to overheat the glass relative to a required tempering temperature since the glass temperature falls before the glass has completely bent to its desired configuration and the glass tempering can be commenced.
Depending on the glass types as well as conditions, the cooling of glass is typically in the order of 10.degree. C.-25.degree. C.
A characterizing feature for this so-called overheating is that the optical errors of glass are accentuated and are more perceivable in the end product.
An object of the invention is to improve the above prior known apparatus in a manner that such detrimental overheating can be omitted thus decreasing the temperature of a glass sheet coming out of a furnace and improving the glass optics.
This object is achieved by means of the invention on the basis of the characterizing features described below.
When, according to the invention, adjustable press rollers are provided above a glass sheet, the gravitational bending is replaced by mechanical press bending, whereby the above object of the invention will be achieved and, furthermore, the accuracy of a glass sheet bending shape will be improved as the bending can be controlled and forced to a desired shape or configuration.
The bending of a piece of glass with a set of upper and lower rollers in a combined bending and tempering station has already been proposed in U.S. Pat. No. 4,822,398. In that publication, however, the bending is effected about a bending axis extending in the glass sheet advancing direction, whereby the rollers abutting both surfaces of a glass sheet during the course of bending travel laterally relative to the glass, i.e. glide along the glass surface in the direction transverse to the advancing direction. This makes it difficult to fulfill the requirement for high optical quality. The present invention relates principally to the bending about an axis extending transversely to the advancing direction. The resilient suspension of press rollers and the pressing force adjustable during the course of bending enable the adaption of the invention also to such benders in which the bending is effected about an axis extending in the advancing direction.